The invention relates to an air flow device for a unit, for example an internal combustion engine, which requires for its operation a given amount of air, in accordance with the preamble of claim 1 and the parallel independent claim 6.
For example, in known internal combustion engines for motor vehicles, to achieve optimal performance air intake systems are preferred which have variable intake sections and thus permit adaptation to various requirements of engine operation. Noise suppression is also important here.
For example, an air intake device for an internal combustion engine is disclosed in DE-OS 40 41 786, in which a controllable shut-off means is present in order to vary the opening through which the aspirated air flows. The shut-off means is in a transverse channel situated between two intake channels and is opened or closed by commands from an electronic control. The commands are dependent upon the rotational speed of the internal combustion engine and on the temperature of the outside air, which is determined by a temperature sensor.
To achieve an improvement of efficiency in the conversion of energy by an internal combustion engine in a range far below the nominal engine power and thus a reduction of the fuel consumption per unit distance, a selective cutoff of cylinders in the internal combustion engine is often practiced. To control engine torque the number of active cylinders can be reduced, in addition to the ordinary throttle adjustment. The cylinders not contributing to the torque continue to run mechanically but are not supplied with fuel. In this cylinder cutout system, however, the pulsation of the aspirated air also changes.
One typical application of cylinder cutout involves changing a 6-cylinder internal combustion engine from 6-cylinder to 3-cylinder operation. Although the suction pulse emitted by each of these cylinders in the air intake device remains unchanged in itself, the cyclical interaction of 6 cylinders results in a different kind of pulsation than that of 3 cylinders. Especially, deep humming sounds are annoying; in view of the space available in a motor vehicle, these low-frequency components can be diminished only by costly reflective sound dampers (e.g., Helmholtz resonators).
But also in many other applications the resonating action of the air intake device plays an important part, and often the available space is a critical factor.